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(Color online) (a) A map of the area where the glider navigated. It was deployed at approximately 40 km from the volcano and recovered near the northern flank of the volcano 2 days later. (b) Glider’s path (solid line) and bathymetry. It progressed toward the volcano at horizontal speed of ∼27 cm/s while repeating a sawtooth profile between 0 and 950 m. The star mark indicates the location of the Hades vent field. The gilder’s data were compared to the West Mata North (WM-N) hydrophone data (a triangle). It was moored at 14°57’27”S, 173°50’53”W approximately 20 km northwest of the volcano summit and recovered before the glider’s operation.
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(Color online) (a) Glider’s acoustic record (2-kHz sampling rate) at approximately 20 km from the volcano during the dive 7 (top: time series; bottom: spectrogram). Wide-band signal from the volcano produced a range-dependent interference pattern as the glider progressed through the water column. The blank period (0.48–0.62 ks) was when the glider reached 950 m and the oil motor was turned on. (b) Fixed AUH hydrophone’s raw record at WM-N (1-kHz sampling rate, mooring depth 1000 m, distance approximately 19 km from the Hades) on March 14, 2010 approximately 2 months prior to the glider operation.
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(Color online) (a) Sound level estimate (averaged over 100–200 Hz) in decibels (re 1 μPa2/Hz) during the glider’s flight. Black dots show the measurement points for the spectral averages along the glider’s sawtooth path. Horizontal axis is a distance from the Hades eruption site. (b) Average propagation loss in decibels between 100 and 200 Hz as a function of distance from the source and depth, based on RAM propagation models. (c) Estimate of the average source level (SL) between 100 and 200 Hz in decibels (re 1 μPa2/Hz 1 m) calculated from the measurement and propagation loss model. The gird size is 50 m (depth) × 1000 m (distance) for all panels.
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An underwater glider with an acoustic data logger flew toward a recently discovered erupting submarine volcano in the northern Lau basin. With the volcano providing a wide-band sound source, recordings from the two-day survey produced a two-dimensional sound level map spanning 1 km (depth) × 40 km(distance). The observed sound field shows depth- and range-dependence, with the first-order spatial pattern being consistent with the predictions of a range-dependent propagation model. The results allow constraining the acoustic source level of the volcanic activity and suggest that the glider provides an effective platform for monitoring natural and anthropogenic oceansounds.
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